1. Field of the Invention
The present invention relates to a novel process for the preparation of carboxylic acid anhydrides, and, more especially, to a process for the preparation of carboxylic acid anhydrides by a novel carbonylation reaction employing a cobalt-based catalyst, it being possible for the subject reaction to be carried out under relatively mild conditions of temperature and pressure.
2. Description of the Prior Art
It is well known to this art that acetic anhydride can be prepared by reacting carbon monoxide with methyl acetate in the presence of a catalyst selected from among cobalt complexes of the general formula: EQU [R.sub.4 A].sub.2 CoX.sub.4,
in which X represents a bromine or iodine atom, A represents a nitrogen or phosphorus atom and R represents a lower alkyl radical, for example (compare U.S. Pat. No. 2,730,546). However, the efficacy of this type of catalyst remains low, even though pressures in the range of from 200 to 650 bars and temperatures on the order of 180.degree. to 190.degree. C. are utilized.
Furthermore, French Pat. No. 1,313,360 describes various carbonylation reactions employing a salt of cobalt tetracarbonyl hydride, in a basic medium, which can all be represented by the equation: EQU RX+CO+BH.fwdarw.RCOB+HX
in which R can be an alkyl radical, X can be a halogen atom and BH represents a molecule containing a mobile hydrogen atom (water, an alcohol, a phenol, a mercaptan, or the like). These reactions are generally carried out at atmospheric pressure or under a pressure of a few tens of bars, and at temperatures on the order of 25.degree. to 50.degree. C.